The formulation of detergent compositions presents a considerable challenge, since effective compositions are required to remove a variety of soils and stains from diverse substrates. In particular, the removal of greasy/oily soils quickly and efficiently can be problematic. While a review of the literature would seem to indicate that a wide selection of surfactants is available to the detergent manufacturer, the reality is that many such materials are specialty chemicals which are not suitable in low unit cost items such as home-use detergent compositions. The fact remains that most home-use detergents still comprise one or more of the conventional ethoxylated nonionic and sulfated or sulfonated anionic surfactants, presumably due to economic considerations.
The challenge to the detergent manufacturer seeking improved fabric cleaning has been increased by various environmental factors. For example, some nonbiodegradable ingredients have fallen into disfavor. Effective phosphate builders have been banned by legislation in many countries. Moreover, many surfactants are often available only from nonrenewable resources such as petrochemicals. Accordingly, the detergent manufacturer is quite limited in the selection of surfactants which are effective cleaners, biodegradable and, to the extent possible, available from renewable resources such as natural fats and oils, rather than petrochemicals.
Considerable attention has lately been directed to noinoic surfactants which can be prepared by using mainly renewable resources, such as fatty esters and sugars. One such class of surfactants includes the N-alkyl polyhydroxy fatty acid amides. Moreover, the combination of such nonionic surfactants with conventional anionic surfactants such as the alkyl sulfates, alkyl benzene sulfonates, alkyl ether sulfates, and the like has also been studied. Indeed, substantial success in the formulation of dishwashing compositions has recently been achieved using the N-alkyl polyhydroxy fatty acid amides. However, even these superior surfactants do suffer from some drawbacks. For example, their solubility is not as high as might be desired for optimal formulations and this is exacerbated at chain lengths of about C.sub.16 and above. At high concentrations in water they can be difficult to handle, store and pump, so additives must be employed in manufacturing plants to control their viscosity and maintain their fluidity.
A suitable method for the manufacture of N-alkly polyhydroxy fatty acid amides having desirable low color and little or no contamination with cyclized by-products, carried out in the presence of organic hydroxy solvents, is disclosed in U.S. Pat. No. 5,194,639, Connor, Scheibel and Severson, issued Mar. 16, 1993.
In order to prevent gelling or solidification of the liquid fatty acid amides, it has generally been found to be necessary to store them at elevated temperatures, and/or to add substantial quantities of organic solvents mentioned in U.S. Pat. No. 5,194,639.
It has now been discovered that certain mixtures of N-alkyl polyhydroxy fatty acid amides can be prepared using low levels of organic solvents, and can be stored at ambient temperatures.
Accordingly, the present invention provides new, highly soluble, highly detersive surfactants which have the additional advantage that they can be prepared in an efficient and effective manner with reduced need for solvents, and which can be stored in the liquid state at ambient temperatures.